Electric Power Tool

ABSTRACT

An electric power tool, in particular an electric hammer, having a drive unit ( 11 ) contained in a housing ( 10 ), an impact mechanism ( 12 ), and a handle ( 13 ), including a cam ( 14 ) that is driven by the drive unit ( 11 ); the impact mechanism ( 12 ) has moving parts ( 15, 16 ). 
     At least two of the moving parts ( 15, 16 ) are able to move inside a separate guide cylinder ( 17 ) that is stationary in relation to the moving parts ( 15, 16 ) and the cam ( 14 ).

PRIOR ART

The present invention is based on an electric power tool according tothe preamble to claim 1.

Know electric power tools, in particular power hammers, have a driveunit in the form of a wobble pin or connecting rod serving as a driveunit for a hammer piston. Drive units of this kind are known, forexample, as crank drives, in which rotary movements of a drive unit,which are transmitted via a crankshaft, are converted into linearmovements of the connecting rod. In this case, the drive unit andcrankshaft are coupled to each other, in particular by means of agearing in the form of a gear-tooth clutch. In rotary hammers andpercussion hammers, the impact mechanism usually functions on the basisof piston or lever movements that are driven by the connecting rod.

There are also older known electric hammer designs that have a pistondrive unit with a slider crank. Slider crank mechanisms are usuallycomprised of a crankshaft equipped with an eccentrically situated crankpin. The connecting rod is structurally integrated into a unit with alifting rod. In order to convert the movement direction, a connection,which is situated between the crankshaft and the connecting rod and isembodied in the form of a crank pin, travels inside a so-called slidercrank. In electric hammers of this kind, a pot-type piston, which canmove back and forth and is connected to a cam, is used as an impactmechanism. A connecting link connected to the pot-type piston, thepiston itself, and the tube in which the striker moves are embodied asintegrally joined to one another. The quality of such electric hammersis not always satisfactory. The crank pin in particular is subjected toan unsatisfactory bearing friction because of the slider crank.

There are also known electric hammers with a pot-type piston impactmechanism, including a steel piston usually made of cast steel with aconnecting link cast onto it. A movement conversion by means of theconnecting link basically corresponds to that of the slider crank, butthe design is less favorable. Primarily, the designer aspect of theknown electric hammers is not taken into sufficient consideration.

ADVANTAGES OF THE INVENTION

An electric power tool according to the present invention, in particularan electric hammer, includes a cam driven by a drive unit and an impactmechanism with moving parts; at least two of the moving parts are ableto move inside a separate guide cylinder that is stationary in relationto the moving parts and the cam. In particular, a piston and a strikercan be provided as the moving parts; the piston that can be moved by thedrive unit is able to actuate the striker in a known fashion via an aircushion. The piston and striker can suitably have the same diameter. Anelectric hammer designed in such a way has a quality equivalent to theknown electric hammers with different impact mechanisms.

Preferably, the piston is connected to the drive unit via a driveelement. The embodiment according to the present inventionadvantageously permits the length of the electric power tool to beshortened. It is thus possible not only for a new designer aspect to betaken into consideration, but also primarily to achieve a slim contourof the electric power tool, as a result of which it is simultaneouslyalso possible to shift the center of gravity and improve the safety ofthe unit's handling.

Preferably, the piston and the drive element are connected to each otherby means of a pin. In a preferred embodiment form, a pin axis of the pinand the rotation axis of the drive unit can be oriented at an angle inrelation to each other, for example of 90°. It is also possible for thepiston and the drive element to be embodied as integrally joined to eachother.

In a modification of the present invention, it is possible to adjust anangle between a longitudinal axis of the impact mechanism and a rotationaxis of the drive unit. If the drive element is embodied in the form ofa cranked rod, then it is advantageously possible to vary an anglebetween the longitudinal axis of the impact mechanism and the rotationaxis of the drive unit. This permits achievement of a new designer-basedconstruction. In addition, this permits an advantageous shifting of thecenter of gravity in that the drive unit is situated centrally inrelation to a longitudinal span of the handle. This permits a reductionof a height of the unit, which has a favorable effect on the weightdistribution in the unit and consequently on its handling. On the whole,the embodiment according to the present invention makes it possible toachieve an elongated, more symmetrical form in comparison to the knownelectric hammers.

In one embodiment form of the present invention, the drive element canbe at least partially comprised of plastic. This advantageously permitsa lightweight construction, which in turn makes a positive contributionto an easier, safe operability.

In order to transmit force between the cam and the drive element, it ispossible for a slider crank to be provided. In an above-describedcranked embodiment form of the drive element, the slider crank islaterally offset in relation to a longitudinal span of the driveelement, which in turn permits advantageous variations in theconstruction of the unit, making use of new designer aspects. If theslider crank is made of plastic, then it is advantageously possible toprevent a premature deflection of the slider crank due to theabove-explained high friction forces. This results in a longer servicelife of the slider crank and thus represents an advantageous costsavings. To further avoid premature wear, a ball is able to move insidethe slider crank.

It is also possible for a connecting link to be provided for thetransmission of force between the cam and the drive element. It ispossible for a sliding block to be provided between the eccentric pinand the connecting link, thus advantageously preventing or reducing anundesirable friction. In lieu of the sliding block, it is also possibleto embody a different intermediate element that functions in the samemanner. The connecting link is preferably embodied as straight. It can,however, also have a different form.

In an alternative embodiment form, the impact mechanism is embodied witha pot-type striker. Alternatively, an impact mechanism can be embodiedwith a pot-type piston, which is able to activate a pot-type striker. Toreduce the weight of the structure, the pot-type piston is preferablycomprised of a light alloy. Alternatively, the pot-type piston can alsobe made of plastic or of a light alloy/plastic composite. This materialcomposition gives the unit a particularly long service life.

DRAWINGS

Other embodiment forms, aspects, and advantages of the present inventionensue from the following exemplary embodiments of the invention shown inthe drawings, independent of their combination in the claims and withoutlimitation as to their universal applicability.

FIG. 1 is a schematic section through one embodiment form of an electricpower tool according to the present invention;

FIG. 2 is a schematic top view of an alternative embodiment form; and

FIG. 3 is a schematic section through another alternative embodimentform.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 is a longitudinal section through an electric hammer, having adrive unit 11 contained in a housing 10, an impact mechanism 12, and ahandle 13. The drive unit 11 drives a cam 14; the drive unit 10 and thecam 14 are coupled to each other in a known manner by means of a gearingin the form of a gear-teeth clutch 20. In order to transmit forcebetween the cam 14 and the drive element 18, a connecting link 32 isprovided. The rotary motion that the drive unit 11 transmits to the cam14 is converted by the connecting link 32 into a linear stroke motion ofthe drive element 18 and is transmitted to an impact mechanism 12.

The impact mechanism 12 includes two moving parts embodied in the formof a piston 15 and a striker 16, which are able to move inside aseparate guide cylinder 17 that is stationary in relation to the movingparts 15, 16. The piston 15 and the striker 16 have the same diameter22. An annular seal 30 is provided between the piston 15 and the guidecylinder 17 and an annular seal 31 is provided between the striker 16and the guide cylinder 17. The piston 15 is connected to the drive unit11 via the drive element 18. The drive element 18 is embodied as acranked rod with a cranked section 26. The longitudinal segments of thedrive element 18 before and after the cranked section 26 are offset fromand parallel to each other. The connecting link 32 connected to a freeend of the drive element 18 is thus laterally offset from the pin 19situated at other free end of the drive element 18. An upper edge of thedrive element 18 ends in this region, approximately at an upper edge ofthe guide cylinder 17. This makes it possible to reduce the length ofthe electric hammer in the region of the handle 13. The drive element 18is at least partially comprised of plastic.

The drive element 18 and the piston 15 are connected to each other bymeans of a pin 19. A pin axis of the pin 19, which extends transverselyto the plane of the drawing, and a rotation axis 21 of the drive unit 11are oriented at an angle of 90° in relation to each other. The linearstroke motion of the drive element 18 generates a compression and avacuum against the piston, which accelerate the striker 16 via an aircushion 29. The striker 16 imparts its energy to an insert tool that isnow shown.

The cam 14 has a cam disk 33, which is connected to the drive element 18via an eccentric pin 34. The eccentric pin 34 is inserted into a slidingblock 35 in order to minimize a friction between the eccentric pin 34and the connecting link 32. The sliding block 35 functions inside theconnecting link 32 of the drive element 18. The connecting link 32 isstraight. The linear stroke motion of the drive element 18, which isconverted by the connecting link 32, has a sinusoidal curve with astraight connecting link 32. It is also possible for the connecting link32 to be embodied in a different form, which correspondingly changes thecurve of the longitudinal movement. This alternative is not shown inFIG. 1.

FIG. 2 is a top view of an alternative embodiment form in which thedesign and function of the individual components corresponds to those inFIG. 1. Elements that are the same have been labeled with the samereference numerals. By contrast with FIG. 1, the drive element 18 andpiston 15 are not connected to each other by means of a pin 19, but areinstead embodied as integrally joined to each other. This eliminates theneed for a longitudinal guide. As opposed to FIG. 1 in which the pistonis cylindrical, the piston 15 in FIG. 2 is disk-shaped. The disk-shapedpiston 15 also has an annular seal 31 along its outer circumference.

FIG. 3 shows another alternative embodiment form of an electric hammeraccording to the present invention, whose design essentially correspondsto the one in FIG. 1, with a cylindrical piston 15 that is connected bymeans of a pin 19 to a drive element 18 embodied in the form of acranked rod. The impact mechanism 12 is embodied as a pot-type piston27; the pot-type piston 27 actuates a pot-type striker 28. A slidercrank 23 is provided to transmit the force between the cam 14 and thedrive element 18. A ball 24 can move inside the slider crank 23.

By contrast with FIG. 1, the drive element 18 is embodied so that itslongitudinal segments before and after the cranked section 26 are notparallel to each other; instead, the drive element 18 bends toward thecam 14. As a result, an angle α that is greater than 90° is formedbetween a longitudinal axis 25 of the guide cylinder 17 and a rotationaxis 21 of the drive unit 11. It is thus possible to adjust the angle αby means of the cranked section 26 of the drive element. With theproposed arrangement, it is possible to vary the angle α between theimpact mechanism 12 and the rotation axis 21 of the drive unit 11. Thisadvantageously makes it possible to achieve a central placement of thedrive unit 11 in relation to a longitudinal span of the handle 13. It issimultaneously possible to reduce a height of the electric hammer,particularly in the region of the handle 13.

This favorably affects a weight distribution in the unit, which is thuseasier to maneuver. The present invention therefore achieves anadvantageous, symmetrical, elongated structure. This makes it possibleto achieve new designer embodiments.

1. An electric power tool, in particular an electric hammer, having adrive unit (11) contained in a housing (10), an impact mechanism (12),and a handle (13), including a cam (14) that is driven by the drive unit(11); the impact mechanism (12) has moving parts (15, 16), wherein atleast two of the moving parts (15, 16) are able to move inside aseparate guide cylinder (17) that is stationary in relation to themoving parts (15, 16) and the cam (14).
 2. The electric power tool asrecited in claim 1, wherein a piston (15) and a striker (16) areprovided as the moving parts.
 3. The electric power tool as recited inclaim 1, wherein the piston (15) is connected to the drive unit (11) bymeans of a drive element (18) embodied as a separate component.
 4. Theelectric power tool as recited in claim 3, wherein the drive element(18) is embodied as a cranked rod.
 5. The electric power tool as recitedin claim 2, wherein the piston (15) and the drive element (18) areconnected to each other by means of a pin (19).
 6. The electric powertool as recited in claim 5, wherein a pin axis of the pin (19) and arotation axis (21) of the drive unit (11) are oriented at an angle toeach other.
 7. The electric power tool as recited in claim 1, whereinthe piston (15) and the drive element (18) are embodied as integrallyjoined to each other.
 8. The electric power tool as recited in claim 3,wherein the drive element (18) is at least partially comprised ofplastic.
 9. The electric power tool as recited in claim 1, wherein thepiston (15) and the striker (16) have the same diameter (22).
 10. Theelectric power tool as recited in claim 1, wherein a slider crank (23)is provided to transmit the force between the cam (14) and the driveelement (18).
 11. The electric power tool as recited in claim 10,wherein a ball (24) is able to move inside the slider crank (23). 12.The electric power tool as recited in wherein it is possible to adjustan angle (α) between a longitudinal axis (25) of the guide cylinder (17)and a rotation axis (21) of the drive unit (11).
 13. The electric powertool as recited in claim 12, wherein it is possible to adjust the angle(α) by means of a cranked section (26) of the drive element (18). 14.The electric power tool as recited in claim 1, wherein the drive unit(11) is situated centrally in relation to a longitudinal span of thehandle (13).
 15. The electric power tool as recited in claim 1, whereinthe impact mechanism (12) is embodied as a pot-type piston (27) and thepot-type piston (27) is able actuate a pot-type striker (28).
 16. Theelectric power tool as recited in claim 15, wherein the pot-type piston(28) is comprised of light alloy.